+/// payment_hash type, use to cross-lock hop
+#[derive(Hash, Copy, Clone, PartialEq, Eq, Debug)]
+pub struct PaymentHash(pub [u8;32]);
+/// payment_preimage type, use to route payment between hop
+#[derive(Hash, Copy, Clone, PartialEq, Eq, Debug)]
+pub struct PaymentPreimage(pub [u8;32]);
+
+type ShutdownResult = (Vec<Transaction>, Vec<(HTLCSource, PaymentHash)>);